1. Field of the Invention
This invention relates to flow meters and more particularly to flow meters able to measure low flow rates while-maintaining high accuracy and line pressure, enabling them to be used in household and other small demand environments.
2. General Background
Many applications exist for replaceable filter cartridges made of various materials that are used in filtration systems to filter water to remove impurities before the water is used. Examples are: point-of-use drinking water equipment, ice machines, and food and beverage vending equipment. Typically, these filter cartridges have a rated life by their manufacturers in terms of a specific volume, i.e. five hundred or one thousand gallons. Naturally, when the manufacturer's rated life has been reached, it is necessary to replace the filter cartridge to maintain water quality. Failure to do so may result in deterioration of water quality and filter cartridge clogging.
Timely maintenance of filter cartridges is especially important in drinking water equipment when health claims are being made. Manufacturers of filter cartridges have recently begun to recommend that filter cartridge replacements be made on a time basis as well as a volume basis, i.e. every six months or once a year, because bacteria tend to grow within the filter cartridges. The growth of bacteria within filter cartridges is related more to the time that the filter cartridge has been used than to the volume of water that has been filtered.
Due to the importance of proper filter maintenance to ensure water quality and a lack of commonly available meters, regulatory agencies which certify water filtration systems require that filter equipment without meters list their useful life at only one-half the actual filtration capacity. Similarly, regulatory agencies require plumbing elements, including flow meters and filter systems, to withstand extreme conditions to avoid catastrophic failure.
While the need exists for a flow meter/monitor to fulfill several needs (namely: track both liquid volume and time of use, as well as to signal the equipment user when end of life is approaching and when end of life has been reached to maintain manufacturers recommended service requirements), market pressures on pricing for such a meter are very sensitive. Such a meter need to be inexpensive, durable, and accurate in order to enjoy a position in the marketplace. Producing accurate flow meters for moderate to low flow rates, at reasonable cost, that exert little back pressure, while meeting regulatory standards, has not been easily or inexpensively accomplished in the past.
Liquid flow meters can also be used in farming, pharmaceutical and chemical processing, the production of soft drinks and other beverages, food processing, other industries, and almost anywhere the flow of liquid needs to be measured.
Common water systems deliver water at a pressure of approximately 60 pounds per square inch. Most filtration systems have a high pressure drop across them, which may decrease the water flow to the consumer. Any flow meter used in such a system must not inhibit the flow of water and must minimize any pressure drop across it. Factors in a flow meter that affect the flow rate and pressure drop across it-include: the impeller chamber size, the impeller wheel size, the nozzle inlet and/or outlet size, the presence or absence of plenums, and the sizing and tapering of ducts, nozzles, and/or attachments.